An insight into investigation of Aircraft Accident & Incident



Aviation is a highly regulated sector. The pilots, flight attendants & engineers are licensed and tested periodically. All others who work in aviation sector are specifically trained for their roles. Each person, including the aircrew have a well defined responsibility. Almost every aspect of Aviation is well documented in  form of Standard Operating Procedure (SOP). All these efforts ensures that air travel is the safest mode of transportation.

Airline operators launch their planes for a commercial flight if and only if it is airworthy and the crew is fit to fly. The weather must be negotiable and the destination airport / alternate airfields must be available. It is said about flight planning "Plan a good flight .... fly a good plan". Flight planning begins much ahead of the flight date. A large number of specialist work in the back offices of Airlines to plan a safe flight. The bottom line - the aircraft is allowed to take off only if it is safe to conduct the flight.

Despite technological advancements, pilots / aircrew do come across in-flight faults or failure of equipment leading to abnormal situations. Most of these circumstances allow the pilot to switch over to a standby system and fly seamlessly. Critical systems may have more than one standby arrangement. A sequential failure of a particular system is unlikely as they are independent of each other. Notwithstanding, the Pilot take each failure seriously. Safety determines if they should continue or divert. When all the standby systems are exhausted and multiple failures occur, the aircraft has to be flown manually or operated in a degraded mode – this rarely happens. Even if it does, the aircrew are trained to deal with most situations by carrying out procedures laid down in their 'Non-Normal' and 'Emergency' check list and land the plane earliest. This is an acceptable norm in aviation since safety is not compromised!!

Ultimately, it is the man behind the machine that matters. Unforeseen circumstances at times limit crew capability. Pilot Incapacitation is one such critical occurrence. The second pilot is capable of landing the plane all by himself despite limitations and added work load when the other cockpit member is unavailable. In fact, the remaining pilot can be visualised as a safety pilot in all such circumstances. Once again safety of the aircraft and passengers is ensured.

Millions of flights are conducted in the manner described above keeping air safety far above the threshold.

The One in a Million Scenario

Yet, one in a million flight lead to an incident or accident – sometimes fatal. Each such occurrence is traumatic for the affected travellers and their dear ones. The occurrences also have the potential to causes flight anxiety to those who come to know of it.

An accident or incident is usually a result of a chain of failures. The failure can be on the part of the aircrew, ATC, engineering staff, the ground operators, the manufacturer, the aircraft designers or the back end office of the Airline to name a few. The good news is that for an occurrence to turn into an accident, multiple failures must occur and the failures must coincide, more commonly known as the Swiss Cheese Model ( An aircraft accident is therefore rare compared to the number of flights flown. But, when it happens, it remains the cause of concern until the reason is established and the correctives are implemented. The little known fact is that each accident is thoroughly investigated and it triggers a slew of measures to avoid recurrence and make air travel even more safer.

The article assumes that an accident / incident has indeed occurred and will try to dwell upon the post occurrence activities – mainly, the accident and incident investigation procedure. It is testimony to how far the aviation community goes to probe air incidents and accidents and make sure that they are completely avoided.

Aviation Accident & Investigation Board

An aviation occurrence that has safety connotations is classified as an 'Accident' or 'Incident' and looked into with all the seriousness it deserves. For ease of understanding, aircraft Accidents and Incidents can be defined as follows -

Definition of Aviation Accident : An occurrence is treated as 'Aircraft Accident' if it results in either a fatality / serious injury to persons on board or on ground, causes substantial damage to the aeroplane or if the aircraft goes missing.

Definition of Aviation Incident : An occurrence other than an Accident is termed as an 'Incident' if it has, or could have affected the safety of a flight.

An Incident is treated as precursor to an impending accident. For that reason, an Incident is seen with same seriousness as an Accident. Fatal accidents receive wider public attention and leave an everlasting inprint on our minds. The Saga of the recent Ethopian 737 MAX crash is a case in point. On the other hand, an incident devoid of fatalities doesn't receive as much media attention and does not remain for too long in memories of air travellers. Unknown to most of the air travellers, all accidents and incidents, irrespective of the media attention, are thoroughly investigated.

International Civil Aviation Organisation, ICAO (, the aviation wing of the United Nations has issued broad guidelines in form of International Standards & Recommended Practices, SARP (Annex 13 to the ICAO Convention) to deal with the subject of Accident & Incident investigation ( The guidelines are uniformly followed worldwide.

ICAO mandates that each country (called Contracting State) has a Aviation Regulatory. The Regulatory is responsible for safe and efficient air operations in their area of responsibility. On the other hand, each country establishes an Accident & Incident Investigation Board (AAIB). As the name suggests, AAIB is responsible to investigate the cause of an accident / incident in its area of responsibility.

AAIB is simply a fact finding body and does not apportion blame. Usually the AAIB are independent of the regulatory. For example, in USA, the FAA ( is the regulatory and NTSB is the Accident Investigation Board ( In India, the regulatory is DGCA ( while AAIB (under the Ministry of Civil Aviation) is a separate entity for Accident / Incident investigation. (

The AAIB is usually an independent federal agency dedicated to promoting aviation safety. In most countries, this agency is mandated by Act of Parliament to investigate civil aviation accidents, determine the probable causes of the accidents, issue safety recommendations, study transportation safety issues, and evaluate the safety effectiveness of government agencies involved in air transportation. The AAIB makes public its actions and decisions through accident reports, safety studies, special investigation reports, safety recommendations, and statistical review.

AAIB usually has a permanent Board comprising aviators, technocrats, technologisticians, medical experts, Psychologist etc. Their workforce is specially trained and completely conversant with the methodologies of Accident Investigation. Aircraft specific specialist are empaneled as Subject Matter Expert (SME) and called in when required.

The Accident & Incident Investigation Process

An AAIB usually swings into action immediately on being sounded of the occurrence in their area of responsibility. Their 'Go Team' reach and secure the site expeditiously, collect and assess the evidence. Immediate safety issues if any are warned to the concerned agencies. They hold fort until the main team begins their work. As soon as their main team finds the likely cause, they issues a Preliminary Report (PR) citing the facts of the case and their broad recommendation. The initial findings may lead to Preliminary Warning (PW) and suggested actions are issued to prevent similar accident before the exact cause of the occurrence is determined. Regulatory are expected to issue Emergency Airworthness Directives. Manufacturers may issue Technical Bulletins to check aeroplanes for similar symptoms. It is not unusual to ground the fleet for corrective measures if the cause is identified and need to be set right to meet flight safety standards before next flight. This is exactly the case with the grounding of the MAX fleet worldwide. On the other hand, it is also possible that the fleet is grounded as a precaution until the cause is identified. In all cases, aviation safety overides commercial consideration!!

The accident / incident Board is usually headed by the country where the accident / incident happens. To make an investigation as thorough as possible, the Investigation Team consist of a range of members comprising specialists from the fields of aeronautics like the airframe, engines, avionics. The Accredited Representatives of the country of registration of the aircraft, the design bureau and the Certification Authorities are usually incorporated in the Board of Inquiry. The representatives of aircraft manufacturers, engine manufacturers, avionics suppliers work in association with the Board. The Aviation Medicine Specialists (AME) and experts in Human Factors also join the investigation. Airline Pilot Association, Flight Attendant Association and ATC representatives have a say in such investigation.

The Board has wide ranging administrative and financial powers. They may question the crew and representatives of the manufacturers and certification authorities. Passengers and witnesses are invited and encouraged to participate in demystifying the occurrence.

The Board can demand any amount of resources to ensure that the accident investigation is thorough and conclusive. Such investigation require immediate salvaging of the parts from occurrence site including remote mountains or sea bed, space for storage and layout of the parts, inspection and scientific analysis of the items in laboratory,  analysis of the Flight Data Recorder / Cockpit Voice Recorder, deliberation and drawing of conclusions. At times, in order to verify a probable cause, they go to the extent of recreating the scenario in another experimental aircraft  or creating a working model of the suspected system. Millions of dollars are spent to investigate aviation accident.

Accident investigation Boards often take a lot of time to come to the conclusion with regard to the cause of the accident. Forensic and laboratory tests, which are often a part of the investigation take a lot of time. The team also investigate the background of the crew and the persons involved in the Air Operations. Criminal investigation may also be mounted alongside. Documentation of the proceedings takes as much time and effort. More than the time lapsed, it is important that the data received from the supporting agency is accurate and authentic and the record keeping is meticulous.

Accident investigation is a scientific process evolved over a time and time tested. In one of the commonest approach, the board investigates the occurrence against an exhaustive list of possible factors that can lead to an accident. This may include design failure, human error, equipment failure, human factors like work overload, environmental factors like icing, bird activities and sabotage to name a few. Under the so called 'Elimination' approach, the Board analyses each possible cause and eliminates them one by one with due justification. This helps them narrow down to the most likely cause of the occurrence.

The members of the board meet often to discuss their observations and findings. Each member has an equal say in the team. The Chairman has a delicate role of coordinating between the team and pushing the Inquiry in the right directions.

Since air safety improvements is the sole consideration of an AAIB investigation, it is independent of any judicial Inquiry that may follow an accident. This gives the Board the required confidence to report the accident in all fairness without any fear of being dragged into controversy or litigation over their opinion.

The final Board proceedings (in many countries) are usually convened in public and citizens as well as the relatives of the victims have a chance to listen to the findings and represent their point of view. The broadcast of final hearing of the famous water landing of US Airways flight 1549 by Capt Sullenberger and his crew will give an insight into how each air crash is probed and eventually concluded.(23 hours of recording over four sessions available at

It is the endeavour of each such AAIB to pin point the likely cause of the occurrence and suggest safety recommendation to all stake holder so that the accident or incident does not repeat. Accidents and incidents are grouped and categorised by AAIB for a better understanding. The data and trend analysis indicates the area of concerns requiring emphasis.

The official report is usually published after adopting it under statute and is made available in public domain. The final report is usually exhaustive and covers every minor detail of the occurence, the findings and the recommendation. A look at the sample is reassuring ( The final report is widely utilised by all stake holders for drawing inferences and implementing improvements in their area of responsibility. All flying aeroplanes are also modified as per recommendation in a given time frame.

That's not all !! Accidents are followed up at Global level. The stake holders meet often under the aegis of ICAO to discuss safety issues. Such periodic review and analysis help stake holders identify the weak links and implement the changes required in their processes to keep pace with technological advancements.


Aviation Safety enhancement is an ongoing process. Each Accident / Incident is a costly mistake that must be avoided at any cost. The investigation by the AAIB is critical for determining the cause of an accident and implementing remedial measures. The existence of AAIB, its processes and the outcome of their effort not only enhances the aviation safety but also reassures the air travellers that flying continues to be the safest way to travel.


The author, Wing Commander K Dinesh is an Aerospace Engineer by training. He is a retired officer of the Indian Air Force. Presently, he practices as an Aviation Safety Consultant with focus on Flight Anxiety removal for air travellers through his venture Cockpit Vista in Mumbai (India). He has helped hundreds of Anxious fliers fight Flight Anxiety and take to the sky again. For more details about him or his initiatives, please visit

Share the joy!!

23 thoughts on “An insight into investigation of Aircraft Accident & Incident”

  1. Nice well described blog. Appreciate retd. wing commander Dinesh’s efforts to pen down a detailed blog on what is an incident and an accident.
    Hope to see more of such blogs on in flight etiquette and how to effectively come across flight fear.

  2. Very interesting blog. Thank you for giving all this info. I’m a layman in this. It’s fantastic to understand the process and know all the efforts taken behind a flight. We generally dont think about all this when we fly. When we read such articles, the respect for you guys increase more! Thank you once again.

  3. My dear dinesh
    Minor SD
    You have said AME for aviation med splst
    Good article for aviation affected personnel
    A few words on followup could be covered
    Modifications bulletins etc necessitated due to accidents / incidents- how their classification and implementation is affected by administrative and financial considerations
    – could bring out that flt safety bulletins are FOC(?) and also mandatory . These may result in grounding causing great loss thus , sometimes leading to declare as nonessential/ non mandatory etc .
    Also do bring out that in our country public hearings are not held. Also , sometimes ownership decides course of action for eg air india govt owned.
    I could not make out your readership. If known comments would be given
    Just back from usa
    Got ip at night and there you were! Regards

    1. Sir,

      Thanks for the critical review.

      As opposed to the common understanding of AME (Aircraft Maintenance Engineer), in the context of our article, AME refers to Aviation Medical Examiner …. a term borrowed from the US Aviation dictionary. I would however modify it in the article for clarity.

      I agree that the follow up of the recommendations of the AAIB is of great significance. I will expand my para to include the follow up actions.

      In the field of Aviation, as of now, US FAA / NTSB and the European EASA are considered the torch Bearers. I wish Indian AAIB also followed NTSB in true spirit of transparency by holding their proceedings the way the NTSB does. Since our AAIB don’t do it at this time, i must mention that as suggested by you.

  4. Very informative article on all aspects of air travel.
    Provides complete information and reassuring to the users.

  5. Excellent article to make all flyers well informed on how everyone is working towards aerospace safety enhancement.

  6. Interesting article Dineshji. Keeping even non-aviation community too engrossed. Simplifying complexities.
    Keep it up?

  7. Very informative information. We are non technical people know just to buy air ticket n travel , but today I got meaning for my travel n enjoyment what I had n shall have . Best compliments

  8. Dear Wg Cdr K Dinesh,

    Thank you for a meticulously and comprehensively compiled blog on Aircraft Accident and Incident Investigation.

    While the post incident/accident investigation seems to be thorough and followed through in right earnest, wonder why design / software flaws such as in the case of the 737 Max ever allowed to happen in the pre-production stage? There seems to be deficiencies in the functioning of the oversight agencies that have been set up by the regulators to monitor design / production / trials before new models are introduced.

    1. Dear Sir,

      We agree.

      US Federal Aviation Administration (FAA) is the Aviation Regulator for US. It is a coincidence that they are the Certification Authority too in case of MAX, since Boeing MAX is a US production. In their role as the Type Certification Authorities of MAX, they have indeed shown poor oversight over the Design and Airworthiness approval of MAX.

      As I said in the article, the AAIB is kept autonomous so that they can investigate occurences and make comments / recommendation on the functioning of any one of these superior formations including the Regulatory and Certification Authority like FAA. Infact, the office of the Inspector General of US Transportation Department has raised flags on the issue of certification of MAX.

      For these reasons, the AAIB (our focus in this article) is simply a fact finding and reporting body – not an oversight agency.

  9. Thanks Dinesh on a good insight on aviation investigations and making us aware about importance of SOP’s and disciplined all around approach in ensuring flight safety.

  10. Very nice article. Though I have done a good bit of air travel, I do have my fears. Such detailed information certainly helps reinforce the confidence in the safety of air travel.

  11. Fantastic article by Retd.Wing Cdr. Dinesh.
    Very interesting to know the facts about flight safety management. Thank you for sharing your blog. Looking forward for more blogs from you. Wish u all the best??

  12. Dinesh..
    Great effort… Very comprehensive and informative paper to tell how everyone involved has a important role to play towards flight safety….!!!

  13. Awesome information given which is helpful for persons related to Aviation directly and indirectly.
    Bhagat Singh Shekhawat

Leave a Reply

Your email address will not be published. Required fields are marked *